Text books often present basic simplified circuits of amplifiers. I decided I needed more power, so I found a circuit, and built an amplifier. I doubled up the output transistors to give it better current handling. At the time I believed in minimalism, so no emitter resistors were fitted.

This is the back view of this minimalist amplifier

This amplifier is minimal in the extreme!, with no power switch, fuses, emitter resistors or biasing for the parallelled output transistors in the output stage. Gain is adjusted with multi-turn pots (for precise matching). Solid core enamelled wire is used through out for wiring.

I was quite happy with this amplifier and it sounded good, although it ran a bit warm. I decided to investigate this a year or so later. I found that the 7918 regulator supplying the opamp (TL072) was oscillating at about 60kHz. This was breaking through, causing a constant 60kHz of about 2 V pk-pk on the output. Adding a capacitor to the output of the regulator (!!!!!) fixed this and the high running temperature, but also bought an unwelcome change to the sound quality. The sound lost some sweetness, and on efficient speakers at low volume a strange squelchy noise appeared.